Vehicles have been developed to perform an idle-stop when idle-stop conditions are met and automatically restart the engine when restart conditions are met. Such idle-stop systems enable fuel savings, reduction in exhaust emissions, reduction in noise, and the like.
In vehicles with such idle-stop systems, an engine may often be restarted following a relatively short idle-stop period, for example following a short wait at the traffic light. To expedite engine restart at the end of the short idle-stop period, high power and fast-turning starters may be used. However, such starters may substantially increase vehicle costs while still not achieving satisfactory restart times. To achieve rapid engine restarts, higher starter accelerations and starter speeds may be needed.
In one example approach, engine restart may be expedited by adjusting a starter voltage, as shown by Heni et al. in WO 03/099605. Herein, during an engine restart, the voltage supplied to an electric starter motor is adjusted by adding or subtracting voltages from a first and second energy store, such as from a battery and a capacitor, using a DC-DC converter.
However, the inventors herein have recognized several potential issues with such a system. As one example, the electrical configuration of Heni's approach may only be advantageous for high-end vehicle systems where the starter and generator are combined. As such, high-end vehicle systems may include brushless starting systems and complex electrical circuits for operating them. Thus, the approach of Heni et al. may add substantial costs, without substantial benefits, to vehicle systems including simpler brushed alternators and starters. As another example, the approach of Heni et al. necessitates the use of a DC-DC converter to add or subtract the voltages from the energy stores in the fixed electrical configuration. The incorporation of components such as the DC-DC converter may also add substantial cost and complexity to a vehicle system.
Thus, in one example, some of the above issues may be addressed by a method of starting an engine in a vehicle, the engine including a starter, the vehicle including a plurality of energy storage devices electrically coupled to the starter. One example embodiment comprises, during a first charging condition, electrically coupling the plurality of energy storage devices in parallel to each other; and during a second discharging condition, electrically coupling the plurality of energy storage devices in series to each other and to the starter to actuate the starter and rotate the engine.
As one example, a first and second energy storage device, such as a battery and a capacitor (for example, an ultra-capacitor or a super-capacitor), may be arranged in an electrical configuration that enables voltage-doubling. Specifically, the battery and the capacitor may be electrically connected in a parallel configuration to each other and to an alternator so as to charge each energy storage device to the same voltage (for example, 12V). Subsequently, when a higher boost voltage is needed (such as, to expedite cranking at engine start), a relay may be used to electrically connect the devices in a series configuration, thereby providing a doubled voltage output (for example, 24V). A diode may be used to ensure an appropriate direction of current flow. Additionally, a charging-rate-controlling resistor may be included in the circuit to enable the charging rate of the capacitor to be varied, for example, based on operating conditions and/or charging opportunities. The electrical configuration may also enable voltage droops and voltage spikes to be absorbed during transient electrical loading. In this way, use of the energy storage devices in the specified electrical configuration may be synergistically applied for both an expedited engine start and for reduced voltage transients during electrical loading.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.